1. Field of the Invention
The field of art to which this invention relates is goniometers. Specifically, this invention relates to micro goniometers for scanning microscopy.
2. Description of the Related Art
With the advent of scanning probe microscopes such as scanning tunneling microscopes (STM) and atomic force microscopes (AFM) several methods have been developed to use their small scale processing capability for high density data storage. In these methods, a probe, or tip interacts with atoms or molecules on a substrate surface to form bumps. The bump forms a bit of information which is represented in a base two (binary) format (i.e., as a 1 or a 0). Movement of the tip is typically controlled by a goniometer. However, goniometers of the prior art limit the movement of the tip to the z-direction, that is, normal to the substrate surface. An example of such a use is disclosed in U.S. Pat. No. 5,327,625 to Clark et al. Although these methods have their advantages, such as high storage density, they are plagued by several disadvantages.
The main disadvantage of scanning probe microscope data storage is that the speed of writing and replication is prohibitively slow. Conventional magnetic and CD-ROM recording rates are approximately 108 and 1.5106 bits/second respectively, while STM atom writing is less than 1 bit/second.
Additionally, writing at the atomic level is usually performed at very cold temperatures and in a vacuum. The equipment used to perform atomic scale writing is therefore very sophisticated and expensive. There are also disadvantages in reading the information written at the atomic level. Atomic scale resolution of the media surface is necessary to read the data. This also requires sophisticated and expensive equipment.
While scanning probe microscopes have advanced the art of microscopy on the atomic scale, their potential has not been fully realized due to the inflexibility of the tip used to interact with the substrate surface.
In addition to high density data storage, scanning probe microscopes, particularly the AFM, have been used in recent years to probe molecular interactions. In this method, the AFM tip of a specific molecular structure is brought close to the substrate surface which is also of a specific molecular structure. The tip is supported on the free end of a cantilever, the deflection of the tip cantilever as a function of tip displacement reveals the force of interaction between the two surfaces (the tip and the substrate) as a function of distance. This force relates to the nature of the interaction. Although the force measurement and the displacement are accurate, the surface area of the interacting surface is not well controlled because the tip angle is fixed and unknown relative to the substrate surface.
Therefore, it is an object of the present invention to provide a goniometer for use with a scanning probe microscope and having a tip capable of tilting in at least one direction.
It is yet another object of the present invention to provide a goniometer for use with a scanning probe microscope and having a tip capable of tilting in at least one direction which can be utilized for high speed, high density writing to a substrate surface.
It is yet another object of the present invention to provide oscillating motion of the tip in the direction normal to the substrate surface and pendular motion about at least one axis parallel to the plane of the substrate surface.
It is yet another object of the present invention to provide a method for testing the interactive forces between two molecular structures with a scanning probe microscope at differing degrees of tip interaction. It is yet another object of the present invention to measure the dynamic interaction between the tip surface and the substrate surface by oscillating the tip.
Accordingly, a goniometer for performing scanning probe microscopy on a substrate surface is provided. The goniometer comprises a cantilever, having a cantilevered end and a supported end, a tip disposed at the cantilevered end of the cantilever, and a block disposed at the supported end of the cantilever. The block has at least one pair of piezoelectric layers and a pair of electrodes disposed about each individual piezoelectric layer. A potential difference is applied between the individual electrodes of a pair of electrodes which causes the corresponding piezoelectric layer to deform. Also provided, is an insulating material disposed between the individual electrodes for insulating the individual electrodes from each other. The individual piezoelectric layers are deformed at different rates resulting in a deformity of the block and tilting of the cantilever and tip connected therewith.
Another aspect of the present invention are methods for testing the interactive forces between two molecular structures with a scanning probe microscopes at differing degrees of tip interaction. The method comprises the steps of providing an AFM tip of a first molecular structure and providing a substrate material of a second molecular structure. The next step comprises bringing the tip in proximity to the substrate surface at an angle relative to the substrate surface, such that a force of interaction exists between the tip and substrate material. The interactive force is then measured and the tip angle is varied. The interactive force is then measured at the varied tip angle. Preferably, the varying and measuring steps are repeated for a plurality of angles until sufficient data is gathered regarding the tip and substrate surface interactions.
A variation of this method is also disclosed where the tip is oscillated normal to the surface of the substrate material to measure the dynamic interaction between the tip molecular structure and the substrate surface molecular structure.